1. Technical Field
The present invention generally relates to radiography. More particularly, the present invention relates to coherent-scatter imaging for radiography using a divergent beam over a wide field of an object to be analyzed.
2. Background Information
Mammography is the primary screening tool for the detection of breast cancer. Improved specificity is desirable because false positives may cause the patient unnecessary trauma and lead to unnecessary biopsies and because false negatives may cause delayed treatment.
Contrast in conventional mammography systems is created when x-rays are removed by absorption and by scattering, which redirects the paths of incident x-ray beams. In conventional radiography systems, a grid of lead ribbons is placed between the patient and x-ray detector to remove the scattered x-rays from the resulting image.
However, it is known that different tissue types characteristically produce coherent scatter at small diffraction angles. If a small tissue sample is irradiated with a pencil beam (i.e., a highly collimated beam) of x-rays, a narrow cone of coherent scatter is produced around the primary beam that is transmitted by the sample. Therefore, it may be possible to obtain additional information about tissue type present in the sample by measuring the cone angle of the coherently diffracted x-ray radiation. Because a highly-collimated pencil beam only illuminates a small area of a subject to be analyzed, the pencil beam must be scanned over an entire area of a subject in order to obtain an image of the entire subject. This presents two problems. One is the time required to completely scan the subject. Thus, a need exists for a radiographic system that reduces the time required to obtain an image of a subject to be analyzed. The second problem is that conventional radiographic systems illuminate a patient with a wide field of x-ray radiation rather than a pencil beam. Therefore, a need exists for a method of detecting coherently-scattered radiation that is compatible with existing wide-field radiographic systems.